Non-aqueous lithium electrochemical cells typically include an anode, an electrolyte comprising a lithium salt that is dissolved in one or more organic solvents and a cathode of an electrochemically active material, typically a chalcogenide of a transition metal. During discharge, lithium ions from the anode pass through the liquid electrolyte to the electrochemically active cathode material of the cathode where the ions are taken up with the simultaneous release of electrical energy. During charging, the flow of ions is reversed so that lithium ions pass from the electrochemically active material through the electrolyte and are plated back onto the anode.
Recently, the lithium metal anode has been replaced with a carbon anode such as coke or graphite intercalated with lithium ions to form Li.sub.x C. In operation of the cell, lithium ions pass from the carbon through the electrolyte to the cathode where it is taken up just as in a cell with a metallic lithium anode. During recharge, the lithium is transferred back to the anode where it reintercalates into the carbon. Because no metallic lithium is present in the cell, melting of the anode does not occur even under abuse conditions. Also, because lithium is reincorporated into the anode by intercalation rather than by plating, dendritic and spongy lithium growth does not occur. Non-aqueous lithium electrochemical cells are discussed in U.S. Pat. Nos. 4,472,487, 4,668,595, 5,028,500, 5,441,830, 5,460,904 and 5,540,741.
Conventional methods of fabricating electrochemical cells typically consist of using organic solvents in making the electrodes and polymeric matrix (e.g., separator). For example, a solid electrolyte containing the polymeric matrix is prepared by curing a mixture comprising an organic solvent and solid matrix forming monomers and/or partial polymers thereof. Alternatively, the solid electrolyte is formed by solvent casting whereby a mixture comprising an organic solvent and a polymer is first coated onto the appropriate substrate. Thereafter, a polymeric film is formed upon removal of the solvent. Electrodes can also be fabricated by similar solvent casting techniques.
As is apparent, conventional methods of preparing electrochemical cell components require the use of significant organic solvents which pose environmental and health risks. These risks are particularly evident in the case of solvent casting since an evaporative step is required to extract the casting solvent (e.g., acetone) prior to insertion of the electrolyte solvent and inorganic salt. The organic solvents must therefore be recovered which further adds to the manufacturing costs.